Preheat oven to 375°F. Heat butter and olive oil in large skillet over medium-low heat. Add onions, salt and thyme. Sauté 25 minutes or until onions are golden brown and soft. Set aside.
Add 2 cups milk and half and half to large saucepan. Bring mixture to boil. Add onion skins. Lower heat and simmer 20 minutes. Remove onion skins and discard.
Meanwhile, combine beef broth and water in large saucepan. Bring mixture to boil. Add pasta and cook 5 minutes. Drain and set aside. In 2-quart baking dish combine pasta, onions and cheese sauce. Mix to combine. Sprinkle bread crumbs and remaining cheese over top. Bake 30 minutes.
*Wisconsin makes several alpine-style cheeses including Grand Cru and Pleasant Ridge Reserve.
Pipette pasta is a pipe-shaped, curved pasta. The pipe is open on both ends, but one end is pinched slightly. Penne pasta or pasta shells could be substituted.